ETT size and depth (pediatric)

Uncuffed internal diameter (mm) = age in years ÷ 4 + 4 (Cole). Cuffed internal diameter (mm) = age in years ÷ 4 + 3.5 (APLS/Motoyama/Duracher). Oral insertion depth at the lips (cm) = age in years ÷ 2 + 12. These are estimates: round the tube diameter to the nearest available 0.5 mm size, keep tubes 0.5 mm larger and smaller on hand, and confirm placement by air-leak test, auscultation, capnography, chest rise, and imaging. A depth cross-check is tube ID (mm) × 3, which should agree with age ÷ 2 + 12 within about 1 cm.

Estimation formulas, not a severity score — no interpretation bands apply (interpretation is intentionally empty). Cuffed constant is pinned to +3.5 (APLS/Motoyama/Duracher 2008, PMID 18184241); the classic Khine +3.0 (PMID 9066329) yields a tube 0.5 mm smaller and is still widely taught — recorded here per the pin-the-constant requirement. Round each raw internal diameter to the nearest manufactured 0.5 mm step and keep tubes 0.5 mm larger and smaller available; the age formulas mis-size a meaningful minority of children (Cole tends to over-size the youngest in range), so always confirm fit clinically (uncuffed air-leak conventionally audible at ~20–30 cmH₂O). Domain is roughly 1–10 (up to ~12) years: below ~1 year, sizing/depth are weight- and gestational-age-based (Merck/NRP table; Kempley 2008, PMID 18372092) and are NOT computed here; above ~12 years use adult sizing. Only the ORAL depth formula is emitted. NEEDS SOURCE (carried from research): the nasal-route depth offset (~+2–3 cm) is not verified from a primary source, and the fixed infant depth steps (~10/11/12 cm) lack primary APLS pagination — neither is implemented here.